The present invention relates to a novel process for the stretch orientation of polyaniline films and fibers. Films of the conducting polymer polyaniline are made by a variety of inexpensive and simple techniques, including electrochemical polymerization and solution casting. The polyaniline films made from these techniques suffer from a deficiency common to most conducting polymers: they possess little or no macroscopic orientation. Although these polymers are microscopically composed of linear chains of atoms, these chains are usually not well-oriented macroscopically. Sometimes oriented bundles of chains or fibrils are present but they are usually positioned randomly with respect to their neighboring chains. For example, in polyacetylene films some orientation can be obtained by stretching the film and causing the fibrils to line up parallel to one another. The orientation was improved when prestretch cis film was heated under stress in a vacuum and additional elongation occurred around the temperature range of 130.degree.-160.degree. C., which coincides with the temperature range for the maximum cis to trans isomerization. H. Shirakawa and S. Ikeda, Synthetic Metals 1, 175 (1979/1980). Alternatively, several elaborate schemes to produce aligned polyacetylene chains have been demonstrated: for example, by polymerization at 10.degree.-13.degree. C. in a liquid crystal medium contained in a magnetic field. K. Akagi, S. Katayama, H. Shirakawa, K. Araya, A. Mukoh and T. Narahara, Synthetic Metals 17, 241 (1987). In even earlier efforts, poly-p-phenylene sulphide was crystallized by stretching at high (250.degree. C.) temperatures. [B. J. Tabor, E. P. Magre and J. Bloom, Erpn. Polymer J., 7, 1127(1971)].
Accompanying this macroscopic alignment are several effects on the physical properties of polyacetylene, all of which have technological value: the electrical conductivity and the optical absorption can become anisotropic with the largest conductivity or absorption being in the direction of stretching. Anisotropy of conductivity and optical absorption and reflection leads to novel devices such as conductors which transmit light polarized perpendicular to the orientation or alignment direction while reflecting parallel polarized light. The tensile strength of polyacetylene film is also improved dramatically by such macroscopic orientation.
Attempts to treat the polyaniline class of polymers in the same manner, at room temperature, as polyacetylene polymers have met with little or no success, despite the disclosures regarding the preparation of polyaniline films in 1986. [M. Angelopoulos, A. Ray, A. G. MacDiarmid and A. J. Epstein, Synth. Met. 21, 21 (1987) (Proc. Vadstena Conf., Aug. 1986); M. Angelopoulos, G. E. Asturias, S. P. Ermer, A. Ray, E. M. Scherr, A. G. MacDiamid, M. Akhtar, Z. Kiss and A. J. Epstein, Mol. Cryst., Liq. Cryst. 160, 151 (1988)].
The alignment of polyaniline films, such as emeraldine films, has been a topic of ongoing research. Stretching of polyaniline films at room temperature by adhering the films to stretchable polyethylene films has been attempted. [A. G. MacDiarmid, et al., Univ. of PA., to be published.] Further, spinning of a conducting form of polyaniline has been attempted and has resulted in fibers. These fibers have been spun at room temperature from solutions in concentrated sulfuric acid. Attempts to stretch these polyaniline films and fibers have been reportedly unsuccessful. A. Andreatta, Y. Cao, J. C. Chiang, A. J. Heeger, and P. Smith, Synthetic Metals, in press.
Therefore, a simple process for the stretch-orientation of polyaniline films and fibers to provide desired technological improvements such as anisotropic electrical conductivity, optical absorption, and tensile strength is in demand and desired.